The present invention relates to improvements in or to the portion of a printing machine for supplying sheets to be printed, and more particularly the invention relates to a printing machine comprising a device for the supply of sheets to be printed with at least two removable feed trays containing the sheets to be printed, extraction means, driven by a single principal motor, to extract the sheets from one of the trays and to propel them in the machine to the printing means, as well as selection means to cause the extraction means to cooperate selectively with one of these trays.
It is customary at present, to equip printing machines or the like with two trays for sheets to be printed, either to facilitate the supply of the machine with a sheet of the same type, or to use selectively sheets of different characteristics (formats and/or colors particularly).
Systems for the extraction of sheets from feed trays and for the selection of the appropriate tray are, in these known machines, driven by an electric motor this special purpose, that is to say, which is different from motors for advancing and printing sheets particularly; a motor with two directions of rotation is associated with a transmission train including two free wheels so as to drive selectively rollers for selecting sheets or starting rolls respectively in the two trays. The motor used has a very high rotary speed, so that the motion-transmitting gears also rotate fast, whence the generation of considerable noise: in addition, the pinions, to be sufficiently strong, must be metallic, which increases their cost and, taking into account the high speeds of rotation, they must be mounted on ball bearings or the like, whence an additional increase in costs.